In the art and practice of high speed lithographic printing, ink is more or less continuously conveyed from a suitable input device by means of a series of coextensive rollers to a planographic printing plate where the image portions of the printing plate accept ink from one or more of the last of a series of inking rollers and transfers a portion of that ink to a printing blanket as a reverse image from which a portion of the ink is transferred in the form of a right reading image to paper or other suitable substrate. It is also essential in conventional lithographic printing processes that dampening water containing proprietary additives be conveyed more or less continuously to the printing plate where by transferring in part to the non-image areas of the printing plate the water operates to keep those non-image areas free of ink.
In practical printing press systems, the ink is continuously made available in varying amounts determined by cross-press column input control adjustments to all parts of the printing plate, image and non-image areas alike; and in the absence of dampening water, the printing plate will accept ink in both the image and non-image areas of its surface.
Lithographic printing plate surfaces in the absence of imaging materials have minute interstices and an over hydrophilic or water-loving character to enhance retention of water rather than ink on the surface of the plate. Imaging the plate creates oleophilic or ink-loving areas according to the desired format that is to be printed. Consequently, when both ink an water are presented to an imaged plate in appropriate amounts, only that ink tending to reside in non-image areas becomes disbonded from the plate. In its simplest view, this action accounts for the continuous ink and water differentiation at the printing plate surface, which differentiation is essential and integral to the lithographic printing process.
Controlling for the correct amount of dampening water input during lithographic printing has been an industry-wide problem ever since the advent of lithography. Doing so requires continual operator attention since each column adjustment of ink input may require a change in dampener input. Balancing the columner ink input across the width of the press with the non-columner or uniform dampener input across the width of the press is at best a compromise. Consequently, depending upon which portion of the image format the operator has adopted as his standard of print quality at any given time during the printing run, he may need to adjust the ink input at correspondingly-located cross-press positions, which inadvertently also changes the water balance at that position. Conversely, the operator may adjust the dampener input for best ink and water balance in one inking column across the press which action may adversely affect the ink and water balance at one or more other cross-press locations. Adjustments such as these tend to occur repeatedly throughout the whole press run, resulting in slight to major differences in the quality of the printed output throughout the run. In carrying out these adjustment operations, the resulting copies may or may not be commercially acceptable, leading to waste in manpower, materials, and printing machine time.
Means for correcting this inherent fault in conventional lithography have been addressed such as by use of keyless inkers; none have achieved industry-wide success. Certain of these methods also involve eliminating the dampening system or eliminating operator control of the dampening system.
Certain commercially successful newspaper printing configurations rely on the inking train rollers to carry dampening water directly to the printing plate. Notable among these are the Goss Metro, Goss Metroliner, and the Goss Headliner Offset printing presses which are manufactured by the Graphic Systems Division of Rockwell International Corporation. In these alternative configurations, the input dampening water is deposited onto the ink of an inking vibrator drum such that both ink and water are subsequently and continuously transferred to the inking form rollers for deposition onto the printing plate. In another variation, the input dampening water is applied in a more-or-less conventional way directly to the printing plate by means of separate dampening rollers and dampening water input system. In systems of either type, regardless of the method whereby the water is introduced, it is well known that some of the water works its way into the ink and back down through the return-side of the inking train of rollers and may ultimately be introduced into the ink input system itself. In any case, these conventional lithographic systems require considerable operator attention to maintain ink and water balance and they produce more product waste than desired.
Keyless inking systems have been disclosed that purport to eliminate operator attention to column control of inking by elimination of adjustable inking keys and to thereby minimize much of the aforementioned disadvantages of conventional lithography. None of these systems adequately addresses both of the major problems encountered in attempting to control keyless lithographic printing. The first of these is that an ink metering method is required that continues to function despite the presence of up to about 40% water in the ink without allowing temporarily-free water that may appear to interfere with the ink-metering function. Secondly, the unused or non-uniform portion of the ink film that is being continuously presented to the printing plate must be continuously scraped-off the return side of the inking system to enable continuous presentation of the uniform ink film to the plate by the input side of the inker. This scraped-off film is not uniform in ink and water composition. Since it would not be economically feasible to continuously discard the unused ink and that ink/water mixture must be homogenized either by selectively removing water from the mixture and returning it to the inking system or by thoroughly intermixing the unused ink with fresh replenishment ink and returning the mixture to the inking system. We have found that water removal is unnecessary and in the present invention means is provided to accommodate the dampening water that is naturally acquired in the unused ink during the practice of more-or-less conventional lithographic printing and thereby achieve simplified keyless inking control capability heretofore not practical or possible.